Nickel-molybdenum bonded titanium nitride-titanium carbide

ABSTRACT

SOLID COMPOSITIONS OF FROM 49.5 TO 94 VOLUME PERCENT TITANIUM NITRIDE, AND 5 TO 49.5 VOLUME PERCENT TITANIUM CARBIDE BONDED WITH FROM 1 TO 15 VOLUME PERCENT OF METAL COMPOSED OF 20 TO 50 VOLUME PERCENT NICKEL AND 50 TO 80 VOLUME PERCENT MOLYBDENUM, THE COMPOSITION HAVING AN AVERAGE GRAIN SIZE OF LESS THAN 2 MICRONS AND A DENSITY OF AT LEAST 99 PERCENT OF THEORETICAL ARE PREPARED BY HOT-PRESSING AN INTIMATE MIXTURE OF FINE POWDERED TITANIUM NITRIDE, TITANIUM CARBIDE AND METAL AT A TEMPERATURE BETWEEN 1650* AND 1900*C. AND A PRESURE BETWEEN 1000 AND 5000 POUNDS PER SQUARE INCH. THE DENSE COMPOSITIONS ARE VERY STRONG AND HARD AND POSSESS A VERY DESIRABLE COMBINATION OF OXIDATION RESISTANCE, WEARRESISTANCE, SCRATCH-RESISTANCE AND CORROSION RESISTANCE.

United States Patent 3,671,201 NICKEL-MOLYBDENUM BONDED TITANIUMNITRIDE-TITANIUM CARBIDE Horacio E. Bergna, Wilmington, Del., assignorto E. I. du Pont de Nemours and Company, Wilmington, Del. N0 Drawing.Filed Nov. 21, 1969, Ser. No. 878,892 Int. Cl. B2215 3/00; C0411 35/52US. Cl. 29182.5 5 Claims ABSTRACT OF THE DISCLOSURE Solid compositionsof from 49.5 to 94 volume percent titanium nitride, and 5 to 49.5 volumepercent titanium carbide bonded with from 1 to 15 volume percent ofmetal composed of 20 to 50 volume percent nickel and 50 to 80 volumepercent molybdenum, the composition having an average grain size of lessthan 2 microns and a density of at least 99 percent of theoretical areprepared by hot-pressing an intimate mixture of fine powdered titaniumnitride, titanium carbide and metal at a temperature between 1650 and1900" C. and a pressure between 1000 and 5000 pounds per square inch.The dense compositions are very strong and hard and possess a verydesirable combination of oxidation resistance, wearresistance,scratch-resistance and corrosion resistance.

BACKGROUND OF THE INVENTION There is considerable art available onmetal-bonded nitride-carbide cutting tools such as US. Pats. No. 1,895959 and 1,996,220 and more recently No. 3,409,416 and No. 3,409,419.However, none of these references disclose titanium nitride and titaniumcarbide bonded with the nickel-molybdenum mixture of this invention.

I have discovered that titanium nitride and titanium carbide bonded withthe above described nickel molybdenum mixtures when not pressed asdescribed herein form dense fine-grained bodies of outstanding strengthwhich are also quite hard and resistant to wear, scratching, oxidationand corrosion.

SUMMARY In summary this invention is directed to refractory compositionsconsisting essentially of from 49.5 to 94 volume percent titaniumnitride, from 5 to 49.5 volume percent titanium carbide and from 1 to 15volume percent of metal consisting essentially of 20 to 50 volumepercent nickel and 50 to 80 volume percent molybdenum, said compositionhaving a density in excess of 99 percent of theoretical and an averagegrain size of less than 2 microns, and to the method of preparing suchsolid solutions by heating homogeneous mixtures of titanium carbide andtitanium nitride powders having a particle size of less than one micronand nickel and molybdenum powders having a particle size of less thanmicrons to a temperature between l650 and 1900 C., preferably betweenl750 and 1850" C. and immediately pressing at a pressure between 1000and 5000 pounds per square inch and then rapidly cooling the resultantcompact.

The resulting dense compositions are useful in making wear resistant andcorrosion-resistant parts of exceptional strength and hardness and canbe fabricated into attractive articles of jewelry.

DESCRIPTION OF THE INVENTION This invention is directed to refractorycompositions consisting essentially of 49.5 to 94 volume percenttitanium nitride, 5 to 49.5 volume percent titanium carbide and from 1to volume percent metal consisting essentially of from to 50 volumepercent nickel and from 50 to 80 volume percent molybdenum, saidcomposition Patented June 20, 1972 ice The titanium nitride and titaniumcarbide suitable for use in preparing the solid solutions of thisinvention should have an average particle size of less than one micronand preferably less than 0.5 micron.

Suitable titanium nitride can be obtained commercially as 325 meshpowder from Materials for Industry, Inc., Ambler, Pa. or ConsolidatedAstronautics Inc., Long Island City, NY. or can be prepared byconventional methods as disclosed in U.S. Pat. No. 3,409,416, in US.Pat. No. 3,409,419 or in the Nitrides Chapter VHI in the book HighTemperature Technology by J. M. Blocher Jr., John Wiley & Sons, N.Y.,1956.

Suitable titanium carbide can be obtained commercially as -325 meshpowder from Materials for Industry Inc., Ambler, Pa. or Cerac Inc.,Butler, Wis., or can be prepared by conventional methods well known tothe art.

If the titanium nitride or titanium carbide obtained has too large aparticle size, it can be reduced by simply millin the titanium nitrideuntil the desired comminution is achieved.

The metal powders suitable for use in this invention should have anaverage particle size of less than 10 microns and preferably less than 2microns.

Suitable nickel powder can be obtained commercially as Mond standardgrade fine nickel powder from International Nickel Co., or can beprepared by conventional methods well known to the art.

Suitable molybdenum powder can be obtained commercially as standardgrade molybdenum powder 325 mesh from Sylvania Electric Products Inc.,or can be prepared by conventional methods well known to the art.

The four components are preferably quite pure and it is particularlyimportant that they be substantially free of impurities such as oxygenwhich have deleterious elfects on the solid solutions. Minor amounts ofimpurities normally picked up in milling or mixing the components havelittle or no deleterious effect on the refractory compositions. Thussmall amounts of low melting metals such as cobalt or iron, or highermelting metals such as tungsten, which are ordinarily encountered inmilling equipment or media, can be tolerated as can small amounts ofrefractory materials such as other carbides, nitrides or oxides whichare encountered in the handling described above.

As pointed out above, the titanium nitride is ordinarily used incompositions of this invention in amounts of from 49.5 to 94 volumepercent. It is preferably used in amounts ranging from 60 volume percentto volume percent as such amounts result in a refractory compositionhaving a very desirable combination of properties and appearance. Whenamounts of titanium nitride range between 60 and 85 volume percent, itis preferred to use from 12 to 30 volume percent of titanium carbide andfrom 3 to 10 volume percent of metal.

It is believed that molybdenum penetrates the titanium carbide latticeand it is preferred that a large excess of metal over that which it isbelieved can be taken up in the titanium carbide lattice not be present.This is so because a large excess of metal reduces corrosion resistance,scratch resistance and hardness of the refractory compositions. It istherefore preferred that there be present in the compositions of thisinvention no more than 1 part by volume of metal per part by volume oftitanium carbide.

Preparation The mixture of component powders are prepared much in themanner described in US. Pat. No. 3,451,791. Suitable titanium nitride,titanium carbide, nickel and molybdenum, as described above, arehomogeneously intermixed, such as by ball-milling, for up to 120 hoursor more. The mixed powders are then hot-pressed at temperatures of from1650 to 1900 C. and preferably between 1750 to 1850 C. and pressures offrom 1000 to 5000 pounds per square inch followed by rapid cooling ofthe compact in the manner described in US. Pat. No. 3,451,791.

Refractory compacts The hot-pressed refractory compacts arecharacterized by a porosity of less than one percent which translatesinto a density of at least 99 percent of theoretical, and an averagegrain size of less than 2 microns. As mentioned above, the preferredcompositions of this invention contain from 60 to 85 volume percenttitanium nitride, from 12 to 30 volume percent titanium carbide, from 3to volume percent metal, and have an average grain size of less than onemicron. The chemical content as well as the physical properties of thecompositions of this invention can be determined by methods well knownin the art and described in detail in the US. Pats. Nos. 3,409,416;3,409,419; 3,413,392, and 3,451,791 referred to above.

The solid solutions of this invention demonstrate a hardness of from 92to about 94 on the Rockwell A scale and a transverse rupture strength offrom about 200,000 to almost 325,000 pounds per square inch. Thiscombination of strength and hardness along with their low porosity, finegrain size and refractory nature make the compositions of this inventionuseful in applications requiring corrosion resistance, oxidationresistance, scratch resistance and wear resistance. They areparticularly useful in cutting and turning metal. In addition theirdistinctive color combined with their resistance to scratching andmarring make them desirable for use in articles of jewelry such as watchcases.

This invention is further illustrated by the following illustrativeexamples wherein parts and percentages are by weight unless otherwisenoted.

EXAMPLE 1 This is an example of a composition containing 65 volumepercent of titanium nitride, 30 volume percent of titanium carbide, 2.5volume percent of molybdenum metal, and 2.5 volume percent of nickelmetal.

The titanium nitride used is of grade 325 mesh available from Materialsfor Industry, Inc., and has a specific surface area of 1.1 square metersper gram as determined by nitrogen adsorption. An electron micrographshows dense particles of irregular shapes with sizes between 1 and about10 microns, the bulk being between 1 and 2 microns. The carbon contentis 0.33 percent and the oxygen content is 0.87 percent. Chemicalanalysis reveals 76.19 percent of titanium and 18.71 percent ofnitrogen.

The titanium carbide powder used has a nominal average particle size of0.6 micron as measured by the Fisher Sub-Sieve Sizer and a specificsurface area of about 10 square meters per gram as determined bynitrogen absorption. This titanium carbide powder milled to 0.6 microngrade is commercially available from the Adamas Carbide Corp.,Kennilworth, NJ. An electron micrograph of a dry mount preparation showsthat the titanium carbide grains are between 0.2 and 3 microns indiameter and sometimes are clustered in the form of loose aggregates.The titanium content is about 77.8 percent, the total carbon content isabout 18.8 percent, the free carbon is around 0.07 percent, and theoxygen analyses indicate the oxygen content may vary between about 0.8to 1.6 percent. Analysis by emission spectroscopy shows that titanium isthe major component and also shows 0.5 to 2 percent molybdenum, 0.5 to 2percent tungsten, 0.5 to 2 percent nickel, 500 to 2500 p.p.m. ofaluminum, 200 to 1000 p.p.m. of cobalt, 300 to 1500 p.p.m. of iron, 300to 1500 p.p.m. of niobium, 200 to 1000 p.p.m. of chromium, 200 to 1000p.p.m. of silicon, to 500 p.p.m. of zirconium, 50 to 250 p.p.m. ofcalcium, 50 to 250 p.p.m. of manganese and 5 to 25 p.p.m. of magnesium.

The molybdenum powder used in current standard grade available fromSylvania Electric Products, Inc., Philadelphia, Pa. and has a grain sizeof less than 325 mesh, a specific surface area as determined by nitrogenadsorption of 0.29 square meter per gram and an average crystallite sizeof 354 millimicrons as determined by X-ray diffraction line broadening.An electron micrograph shows the molybdenum powder consists of grains /2to 3 microns in diameter clustered together in open aggregates. Chemicalanalysis of the powder reveals 0.2 percent oxygen and no otherimpurities over 500 p.p.m.

The nickel used is a fine powder, available from International NickelCo., containing 0.15 percent carbon, 0.07 percent oxygen, and less than300 p.p.m. iron. The specific surface area of the nickel powder is 0.48square meters per gram and its X-ray diffraction pattern shows onlynickel, which from the line broadening has a crystallite size ofmillimicrons. Under electron microscope, the powder appears as aggregategrains 1 to 5 microns in diameter.

The powders are milled by loading 6000 parts of preconditionedcylindrical cobalt-bonded tungsten carbide inserts, inch long and inchin diameter, into a 1.3 liter steel rolling mill about 6 inches indiameter, also charged with 290 parts of Soltrol 130 saturatedparaffinic hydrocarbon, boiling range -210" C. The mill is then chargedwith 105.9 parts of titanium nitride, 44.50 parts of titanium carbide,7.6 parts of molybdenum powder, and 6.6 parts of nickel powder, all ofthem as above described.

The mill is then sealed and rotated at 90 revolutions per minute for 5days. The mill is then opened and the contents emptied while keeping themilling inserts inside. The mill is then rinsed out with Soltrol 130several times until all of the milled solids are removed.

The milled powder is transferred to a vacuum evaporator, and the excesshydrocarbon is decanted off after the suspended material has settled.The wet residual cake is then dried under vacuum with the application ofheat until the temperature within the evaporator is between 200 and 300C., and the pressure is less than about 0.1 millimeter of mercury.Thereafter the powder is handled entirely in the absence of air.

The dry powder is passed through a 70 mesh screen in a nitrogenatmosphere, and then stored under nitrogen in sealed plastic containers.

A consolidated billet is prepared from the powder by hot pressing thepowder in a cylindrical graphite mold having a cavity with a squarecross-section 1 inches X 1 inches and fitted with opposing close-fittingpistons. One piston is held in place in one end of the mold cavity while31 parts of the powder are charged to the cavity under nitrogen andevenly distributed by rotating the mold and tapping it lightly on theside. The upper piston is then put in place under hand pressure. Theassembled mold and contents are then placed in a vacuum chamber of avacuum hot press, the mold is held in a vertical position, and thepistons extending above and below are engaged between opposing graphiterams of the press under pressure of about 600 pounds per square inch.Within a period of a minute the mold is raised into the hot zone of thefurnace at 1175 C. and at once the furnace temperature is increased to1800 C. in 10 minutes, and the temperature of the mold is held at 1800C. for another 2 minutes to ensure uniform heating of the sample. Apressure of 4000 pounds per square inch is then applied through thepistons for four minutes. Immediately after pressing, the mold andcontents, still being held between the opposing rams, is moved out ofthe furnace into a cool zone where the mold and contents are cooled todull red heat in about minutes.

The mold and contents are then removed from the vacuum furnace and thebillet is removed from the mold and blasted with abrasive grit to removeany adhering carbon.

Density of the finished piece as determined by accurate weighing andmeasurement of the dimensions is 5.48 grams per cubic centimeter, whichcorresponds to the theoretical density.

The hot pressed composition is essentially nonporous when examined under1000 magnification. This property is important since nonporous materialsare more corrosion resistant than porous materials of the same chemicalcomposition. Structurally the composition consists of an extremely finenetwork. The porosity based on optical micrographs is Al/A2 on the ASTMscale of porosity.

Electron micrographs indicate a very fine grain structure, few grainsexceeding 1 or 2 microns in size. Electron micrographs show aninter-granular or matrix phase. The micrograph gives the appearance thatthe metal phase has completely wet the titanium carbide-titanium nitridephase or phases.

The specimen is very tough and does not break or chip when droppedfreely to a hardwood floor from a height of 7 feet.

The sample is polished by pressing its faces firmly against rotatingdiamond impregnated cloth discs. A Beuhler polishing machine is employedfor this operation. A 400 grit diamond wheel is used at 1175 revolutionsper minute in the first polishing step and a 1000 grit diamond at 550revolutions per minute is used in a second, finishing step.

The sample polished in this manner has an attractive ornamentalappearance with a golden color.

A second sample of the same size is fabricated as above indicated andcut so that 0.070 inch x 0.070 inch square bars for transverse rupturestrength are separated from each side of a center piece. Portions of thesample are used for indentation hardness tests and for other productcharacterization. The average transverse rupture strength as measured bybending the 0.070 inch x 0.070 inch test bars on a W; inch span is about300,000 pounds per square inch. The hardness is 93.0 on the Rockwell Ascale.

One of the bars used for transverse rupture measurement is crushed andground up in a carbon steel mortar and the powder thus obtained is usedin X-ray diffraction analysis. The X-ray diagram obtained shows a strongface centered cubic pattern with a lattice parameter of 4.2678. Thispattern corresponds to a titanium nitride-titanium carbide solidsolution. The lattice parameters of face centered cubic titanium nitrideand titanium carbide are about 4.24 and about 4.32, respectively. Alllattice parameters are given in kX units.

The composition of this example shows excellent oxidation and corrosionresistance, resistance to thermal shock, resistance to scratching, andlow reactivity with metals.

The unusual combination of high strength and high hardness added to theabove mentioned characteristics makes the composition of this example anexcellent material for wear parts, corrosion resistant parts and cuttingtools for machining metals.

Polished specimens of this composition can also be used as articles ofjewelry.

EXAMPLE 2 The procedure of Example 1 is repeated except that thecomponents are used in amounts to give a composition containing 88.5volume percent titanium nitride, 10 volume percent titanium carbide, 1volume percent molybdenum metal and 0.5 volume percent nickel.

Actual amounts loaded in the 1.3 liter steel mill are 144.20 parts oftitanium nitride powder, 14.81 parts of titanium carbide powder, 3.66parts of molybdenum metal powder, and 0.89 part of nickel metal powder.

A square billet prepared as in Example 1 which has a cross-section of 1%inches and about 0.300 inch in thickness is cut so that specimens 0.070inch x 0.070 inch x about 1 inch are obtained from both sides of acenter piece.

The bars are used for transverse rupture strength meas urements and thevalue obtained is 275,000 pounds per square inch. The rest of the sampleis used for Rockwell A hardness measurement and for other tests. AverageRockwell A value obtained is 93.2.

The density is found to be 5.45 grams per cubic centimeter, which isover 99 percent of the theoretical density.

The composition of this example shown excellent oxidation and corrosionresistance, resistance to thermal shock, resistance to scratching, andlow reactivity with metals.

The unusual combination of high strength and high hardness added to theabove mentioned characteristics makes the composition of this example anexcellent material for wear parts, corrosion resistant parts, andcutting tools for machining metals.

Polished specimens of this composition can also be used as articles ofjewelry.

EXAMPLE 3 The procedure of Example 1 is repeated except that thecomponents are used in amounts to give a composition containing 50volume percent titanium nitride, 36 volume percent titanium carbide, 7volume percent molybdenum metal and 7 volume percent nickel metal.

The actual amounts loaded into the 1.3 liter steel mill are 81.43 partsof titanium nitride powder, 53.32 parts of titanium carbide powder,21.40 parts of molybdenum metal powder and 18.67 parts of nickel metalpowder.

A consolidated billet is fabricated by hot pressing, and is tested asindicated in Example 1.

The average transverse rupture strength measured is 315,000 pounds persquare inch and the average Rockwell A hardness is 92.7.

The density is found to be 5.83 grams per cubic centimeter, whichcorresponds to the theoretical density.

The composition of this example shows excellent oxidation and corrosionresistance, resistance to thermal shock, resistance to scratching, andlow reactivity with metals.

The usual combination of high strength and high hardness added to theabove mentioned characteristics makes the composition of this example anexcellent material for wear parts, corrosion resistant parts, andcutting tools for machining metals.

EXAMPLE 4 The procedure of Example 1 is repeated except that thecomponents are used in amounts to give a composition containing 45volumes percent titanium carbide, 50 volume percent titanium nitride, 3volume percent molybdenum metal and 2 volume percent nickel metal.

The actual amounts loaded into the 1.3 liter steel mill are 66.68 partsof titanium carbide powder, 81.44 parts of titanium nitride powder, 9.17parts of molybdenum metal powder and 5.33 parts of nickel metal powder.

A consolidated billet is fabricated by hot pressing, and is tested asindicated in Example 1.

Average transverse rupture strength measured is 260,000 pounds persquare inch and average Rockwell A hardness is 93.2.

The density is found to be 5.38 grams per cubic centimeter, which isover 99 percent of the theoretical density.

The composition of this example shows excellent oxidation and corrosionresistance, resistance to thermal shock, resistance to scratching, andlow reactivity with metals.

The unusual combination of high strength and high hardness added to theabove mentioned characteristics makes the composition of this example anexcellent material for wear parts, corrosion resistant parts and cuttingtools for machining metals.

I claim:

1. A hot-pressed refractory metal-bonded solid solution of titaniumnitride and titanium carbide consisting essentially of 49.5 to 94 volumepercent titanium nitride, to 49.5 volume percent titanium carbide andfrom 1 to volume percent metal consisting essentially of from to volumepercent nickel and from 5 0 to 80 volume percent molybdenum, saidmetal-bonded solid solution having a density in excess of 99 percent oftheoretical, an average grain size of less than 2 microns, a hardness offrom about 92 to about 94 on the Rockwell A scale, and a transverserupture strength greater than about 200,000 pounds per square inch.

2. A refractory metal-bonded solid solution of claim 1 in which theaverage grain size is less than 1 micron.

3. A refractory rnetal-bonded solid solution of claim 1 wherein volumepercentage of titanium carbide exceeds the volume percentage of metal.

4. A refractory metal-bonded solid solution of claim 1 in which thevolume percent of titanium nitride is to 85, the volume percent oftitanium carbide is 12 to 30, and the volume percent metal is from 3 to10*.

5. A refractory metal-bonded solid solution of claim 4 in which theaverage grain size is less than 1 micron.

References Cited UNITED STATES PATENTS OTHER REFERENCES Kingery, W. D.:Hot-Pressing of Ceramics, in Ceramic Fabrication Processes; New York(1958), pp. 153-5, 161-3.

TOBIAS E. LEVOW, Primary Examiner W. R. SATTERFIELD, Assistant ExaminerUS. Cl. X.R.

